The present invention relates to a device for fastening and sealing a metering valve in an internal combustion engine fuel injector.
Known injectors normally comprise a hollow body supporting the nozzle; and an axial cavity at atmospheric pressure, in which slides a rod controlling the nozzle. The rod is controlled hydraulically by a metering valve comprising a valve body having a control chamber supplied with pressurized fuel and which discharges into a discharge chamber. The valve body is normally substantially cylindrical, and has a flange which is engaged by a ring nut for fastening the valve body to the hollow body.
In known injectors, the valve body has an annular cavity for distributing fuel to the control chamber and which is therefore also at high pressure, so that the valve body must be connected to the hollow body by means of a sealing device between the pressurized annular cavity on one side and the axial cavity and discharge chamber at atmospheric pressure on the other.
For this purpose, the valve body flange normally rests on a shoulder of the hollow body; and at least one annular seal is provided between the cylindrical wall of the valve body and the hollow body seat, and normally rests on a shoulder of the seat. To ensure effective sealing, the seal is so sized as to fit tightly onto the surface of the valve body, which, for technical reasons, has a radial clearance of 5 to 35 microns with respect to the seat.
During operation of the injector, the high fuel pressure--about 1350 bar--in the distribution cavity tends to push, i.e. extrude, the seal inside the gap between the valve body and its seat, thus resulting in the formation of extrusion rings and in wear of the seal. The pressurized fuel, in turn, leaks increasingly through the extrusion rings, thus reducing the difference in pressure and producing friction-induced heat, which further impairs the resistance of the seal, which begins to fray and must therefore be replaced frequently.